I have a photo where a person was shot with a key light of f8.
There is also a fill light. What I want to do is figure out what the
setting was on the fill light by looking at the solid color shirt
histogram. The shirt is the same color all the way around. I converted
the photo to CIE color / Lab color and am looking at the Lightness.
When I do a histogram on the dark side and on the light side I get
these numbers. 126 for light and 24 for the dark.

My question is what is the stop for the fill light, if the key was f8.

Regards
Chuck